This invention relates to a fuel supply control system for internal combustion engines at acceleration, and more particularly to a control system of this kind which can properly control an accelerating increment of fuel supplied to the engine during acceleration in dependence on the reduction gear ratio of a transmission connected to the engine.
A fuel supply control method of this kind has conventionally been proposed, e.g., by Japanese Provisional Patent Publication (Kokai) No. 60-3458, which determines an accelerating increment of fuel supplied to an internal combustion engine when the engine is in a predetermined accelerating condition, by selecting a table from among a group of tables of accelerating fuel increments, depending upon whether or not interruption of fuel supply (fuel cut) was effected immediately before the engine enters the predetermined accelerating condition as well as upon the rotational speed of the engine, and reading an accelerating fuel increment from the selected table in accordance with a rate of change in the opening degree of the throttle valve, to thereby obtain good driveability of the engine satisfying the driver's demand for acceleration.
However, the proposed method has the disadvantage that when it is applied to an engine which is designed to provide high torque even in a low rotational speed region, desired driveability of the engine cannot be obtained over a wide range of the reduction gear ratio assumed by a transmission connected to the engine.
In general, the degree of the driver's demand for acceleration of the vehicle varies depending upon an operating condition in which the engine is operating. Specifically, when the vehicle is running with a small reduction gear ratio of the transmission selected, i.e., with the transmission in a high speed gear position such as one of third through fifth speed, the driver usually wants the vehicle to exhibit high acceleration response and he heavily depresses the accelerator pedal to rapidly increase the opening degree of the throttle valve. On the other hand, when the vehicle is running with a large reduction gear ratio of the transmission selected, i.e., with the transmission in a low speed gear position such as first speed or second speed, the driver usually requires moderate acceleration of the vehicle so that he lightly depresses the accelerator pedal to slowly increase the opening degree of the throttle valve.
However, the proposed method does not contemplate the above-mentioned difference in required acceleration response depending upon the gear ratio. Therefore, when the proposed method is applied to an engine of the type providing high torque at low speeds, if the acceleration fuel increment is set so as for the engine to exhibit sufficient acceleration response when the transmission is in a high speed gear position, the acceleration response of the engine becomes excessively high when the transmission is in a low speed gear position even if the opening degree of the throttle valve is increased at a small rate, thereby causing unsmooth or awkward running of the vehicle as it is repeatedly accelerated and decelerated, e.g., in a traffic snarl, that is, degrading the driveability.
Conversely, if the accelerating fuel increment is set so as for the engine to exhibit moderate acceleration response when the transmission is in a low speed gear position, the engine will show insufficient acceleration response when the transmission is in a high speed gear position, thus failing to provide desired accelerability of the engine.